Multiple choice

A takes 8 hours more than the time taken by B to cover a distance of 160 km. If A doubles his speed, he takes 3 hours more than B to cover the same distance. The speed (in km/h) of B is:

  1. 75

  2. 70

  3. 72

  4. 80
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let B's speed be v km/h and time be t hours. Then vt = 160. A takes 8 hours more, so A's normal speed = 160/(t+8). When A doubles speed, time becomes 160/[2×160/(t+8)] = (t+8)/2. This equals t+3, so (t+8)/2 = t+3, giving t = 2 hours. Therefore v = 160/2 = 80 km/h.

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